Influenza A is an enveloped negative single-stranded RNA virus that infects a wide range of avian and mammalian species. Human infection mainly involves the upper and lower respiratory epithelial tracts, with approximately 20% of children and 5% of adults worldwide experiencing symptomatic influenza each year. During an average epidemic season in the United States, an influenza season of typical severity results in >100,000 cases requiring hospitalization and >30,000 deaths, with 90% of the morbidity and mortality occurring in the elderly (?65 years of age). Use of a conventional vaccine strategy for control of influenza A may lead to primary vaccine failure because of vulnerability to antigenic drift and emergence of unmatched epidemic strains. A vaccine strategy employing an influenza antigen which is less susceptible to antigenic variation would be a major improvement. The overall purpose of this proposal is the development and testing of a novel HA stem trimer antigen produced with the SutroVax cell free expression technology. The antigen has been produced in our laboratory using a commercially viable process at yields (~1 g/L) which indicate this could be developed into a prophylactic vaccine product. The specific goals of this proposal are to 1) produce and purify a non-his tagged version of the HA stem; 2) determine immunogenicity and protection in mice using representative H1 and H3 strains. Accomplishment of these goals will setup a Phase II SBIR which will focus on the scale-up and testing of the candidate vaccine in ferrets and non-human primates prior to Phase I human clinical trials.